After the recent changes nobody use siglock to read the values protected
by stats_lock, we can kill spin_lock_irq(&current->sighand->siglock) and
update the comment.

With this patch only __exit_signal() and thread_group_start_cputime() take
stats_lock under siglock.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/exit.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 3988a02efaef..dfb963d2f862 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1127,17 +1127,14 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
 		 * and nobody can change them.
 		 *
 		 * psig->stats_lock also protects us from our sub-threads
-		 * which can reap other children at the same time. Until
-		 * we change k_getrusage()-like users to rely on this lock
-		 * we have to take ->siglock as well.
+		 * which can reap other children at the same time.
 		 *
 		 * We use thread_group_cputime_adjusted() to get times for
 		 * the thread group, which consolidates times for all threads
 		 * in the group including the group leader.
 		 */
 		thread_group_cputime_adjusted(p, &tgutime, &tgstime);
-		spin_lock_irq(&current->sighand->siglock);
-		write_seqlock(&psig->stats_lock);
+		write_seqlock_irq(&psig->stats_lock);
 		psig->cutime += tgutime + sig->cutime;
 		psig->cstime += tgstime + sig->cstime;
 		psig->cgtime += task_gtime(p) + sig->gtime + sig->cgtime;
@@ -1160,8 +1157,7 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
 			psig->cmaxrss = maxrss;
 		task_io_accounting_add(&psig->ioac, &p->ioac);
 		task_io_accounting_add(&psig->ioac, &sig->ioac);
-		write_sequnlock(&psig->stats_lock);
-		spin_unlock_irq(&current->sighand->siglock);
+		write_sequnlock_irq(&psig->stats_lock);
 	}
 
 	if (wo->wo_rusage)
-- 
2.25.1.362.g51ebf55

On Tue, Jan 23, 2024 at 7:35 AM Oleg Nesterov <oleg@redhat.com> wrote:
>
> After the recent changes nobody use siglock to read the values protected
> by stats_lock, we can kill spin_lock_irq(&current->sighand->siglock) and
> update the comment.
>
> With this patch only __exit_signal() and thread_group_start_cputime() take
> stats_lock under siglock.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
>  kernel/exit.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 3988a02efaef..dfb963d2f862 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -1127,17 +1127,14 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
>                  * and nobody can change them.
>                  *
>                  * psig->stats_lock also protects us from our sub-threads
> -                * which can reap other children at the same time. Until
> -                * we change k_getrusage()-like users to rely on this lock
> -                * we have to take ->siglock as well.
> +                * which can reap other children at the same time.
>                  *
>                  * We use thread_group_cputime_adjusted() to get times for
>                  * the thread group, which consolidates times for all threads
>                  * in the group including the group leader.
>                  */
>                 thread_group_cputime_adjusted(p, &tgutime, &tgstime);
> -               spin_lock_irq(&current->sighand->siglock);
> -               write_seqlock(&psig->stats_lock);
> +               write_seqlock_irq(&psig->stats_lock);
>                 psig->cutime += tgutime + sig->cutime;
>                 psig->cstime += tgstime + sig->cstime;
>                 psig->cgtime += task_gtime(p) + sig->gtime + sig->cgtime;
> @@ -1160,8 +1157,7 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
>                         psig->cmaxrss = maxrss;
>                 task_io_accounting_add(&psig->ioac, &p->ioac);
>                 task_io_accounting_add(&psig->ioac, &sig->ioac);
> -               write_sequnlock(&psig->stats_lock);
> -               spin_unlock_irq(&current->sighand->siglock);
> +               write_sequnlock_irq(&psig->stats_lock);
>         }
>
>         if (wo->wo_rusage)
> --
> 2.25.1.362.g51ebf55
>

Signed-off-by: Dylan Hatch <dylanbhatch@google.com>